One of storage batteries is a redox flow battery (hereinafter, may be referred to as an “RF battery”) in which a battery reaction is conducted by supplying electrolytes to electrodes. The RF battery has characteristics such as (1) ease of output increase and capacity increase to a megawatt (MW) level, (2) a long life, (3) capability of accurately monitoring the state of charge (SOC) of the battery, and (4) high design freedom such that battery output and battery capacity can be independently designed, and is expected to be a suitable storage battery for stabilization of power systems.
An RF battery includes, as a main component, a battery cell including a positive electrode to which a positive electrode electrolyte is supplied, a negative electrode to which a negative electrode electrolyte is supplied, and a membrane disposed between the two electrodes. A battery cell is typically formed by using a cell frame including a bipolar plate on which electrodes are disposed and a frame body which is provided on the outer periphery of the bipolar plate. A large-capacity RF battery uses a cell stack including mainly a layered body formed by stacking a cell frame, an electrode of one polarity, a membrane, and an electrode of the other polarity in this order repeatedly a plurality of times.
The layered body is sandwiched between a positive electrode supply/drainage plate and a negative electrode supply/drainage plate for supplying unreacted electrolytes to their respective electrodes and discharging electrolytes used in battery reactions from their respective electrodes, and further sandwiched between a pair of end plates. The end plates are fastened with long bolts and nuts. The stacked state is maintained by the fastening force acting in the stacking direction. Furthermore, the fastening force enables a sealing member disposed between two adjacent frame bodies to maintain the space between the frame bodies in a fluid-tight manner so as to prevent leakage of electrolytes.
Patent Literature 1 discloses a rectangular frame body having a rectangular window provided in the central part thereof, the frame body is horizontally long, and the ratio of the length of the long side to the length of the short side at the outer periphery of the frame body (long side/short side), i.e., the aspect ratio, exceeds 1. Patent Literature 1 also discloses that the frame body is formed of a pair of frame pieces each having a window, and the periphery and its vicinity of a bipolar plate are sandwiched between opening peripheries and their vicinities of the frame pieces, followed by fusion bonding to integrate the bipolar plate and the frame body with each other.